The present invention relates to a method and an apparatus of testing quench-hardening, and particularly relates to a method of testing quench-hardening suitable for non-destructive inspection of quench-hardened depth or a quench-hardening pattern of a hollow or solid member subjected to an induction hardening (high-frequency quench-hardening) treatment in at least one of inner and outer circumferential surfaces of the member.
Generally, hollow or solid parts such as inner and outer wheels of hub units, outer races and inner races of constant velocity joints, shafts for cars, and so on, are subjected to surface quench-hardening with high-frequency energy.
As the method of testing the degree of the quench-hardening, the following methods are known:
(1) A method in which a change in the macro structure of steel due to quench-hardening is detected as a change in magnetic characteristics to thereby estimate the quench-hardened depth (Japanese Patent Examined Publication No. Sho-41-2435); PA1 (2) A method in which a change in the macro structure of steel is detected as a change in sound velocity of a ultrasonic wave to thereby estimate the quench-hardened depth (Japanese Patent Unexamined Publication No. Sho-53-32054); and so on. PA1 (3) Thermal expansion of heated parts which are being subjected to quench-hardening is measured to thereby determine the quench-hardened macro structure (Japanese Patent Examined Publication No. Hei-2-23827).
Further, as a method of estimating the quench-hardened depth while parts are being heated, the following methods are known:
Of the above conventional quench-hardening testing methods, the methods (1) and (2) are limited in that the estimation can be performed only on the quench-hardening in the outer circumferential surfaces of parts which are simple in shape and those methods cannot be applied to the quench-hardening estimation in the case where the parts are complicated in shape or in the case where the quench-hardening test is to be performed on the inner circumferential surfaces of hollow parts. The method (3), on the other hand, is limited in that it cannot be applied to the quench-hardening depth estimation on parts after cooling while it is effective in monitoring a quench-hardening heat treatment (particularly, a temperature of the quench-hardening and a holding time). Further, there is a problem that the depth distribution of a quench-hardened layer cannot be measured.